The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium. The heart rests obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and typically projects farther into the left than into the right half of the thoracic cavity so that about one-third is situated on the right and two-thirds on the left of the median plane. The heart is subdivided by septa into right and left halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium, the lower the ventricle. The heart therefore consists of four chambers; the right and left atria, and right and left ventricles, with one-way flow valves between respective atria and ventricles and at the outlet from the ventricles.
The atrioventricular heart valves (i.e., the tricuspid and mitral valves) are located in the center of the heart between the atria and the ventricles of the heart, and play important roles in maintaining forward flow of blood. Atrioventricular valve dysfunction is also commonly known as “regurgitation” and affects well over one million people globally. The mitral and tricuspid valves are defined by fibrous rings of collagen, each called an annulus, which forms a part of the fibrous skeleton of the heart. The annulus provides peripheral attachments for the two cusps or leaflets of the mitral valve (called the anterior and posterior cusps) and the three cusps or leaflets of the tricuspid valve. The free edges of the leaflets connect to chordae tendinae from more than one papillary muscle. In a healthy heart, these muscles and their tendinous chords support the mitral and tricuspid valves, allowing the leaflets to resist the high pressure developed during contractions (pumping) of the left and right ventricles.
Although valve regurgitation often occurs due to the dilatation of the valve annulus, mitral and tricuspid valve function and competency frequently depend on the fine geometric and functional integrity of the valve's supporting structures, such as, for example, the associated subvalvular apparatus. The subvalvular apparatus of these heart valves include, among other things, the associated chordae tendinae and papillary muscles.
As seen in FIGS. 1 and 2, the mitral valve (MV) is a two-leaflet (or bicuspid) structure of connective tissue separating the left atrium (LA) from the left ventricle (LV). The mitral valve functions to maintain blood flow in one direction, i.e., from the left atrium toward the left ventricle during ventricular relaxation or diastole, while preventing back flow in the opposite direction during ventricular contraction or systole. The anterior leaflet (AL) and posterior leaflet (PL) are separated by the anterior commissure (AC) and posterior commissure (PC). The bases of the two valve leaflets are attached to a circular fibrous structure of the heart called the mitral annulus (AN), and the leaflet free edges are attached to chordae tendinae arising from the papillary muscles of the left ventricle. An anterior leaflet (AL) is relatively large and attaches to the anterior segment of the annulus, while a posterior leaflet (PL) is smaller but extends further circumferentially and attaches to the posterior segment of the annulus. The posterior leaflet presents three scallops identified as P1, P2, P3, while the corresponding non-scalloped parts of the anterior leaflet are identified as A1, A2, and A3, according to Carpentier's segmentation.
The tricuspid valve also has subvalvular structures, but is a tricuspid (i.e., three cusp or leaflet) structure as opposed to the bicuspid structure of the mitral valve. Some mitral and tricuspid valve replacement procedures involve the removal of these subvalvular structures. However, the subvalvular structures may play a role in maintaining the proper shape of the ventricles, and thus their preservation may be desirable, depending on the particular circumstances.
When the left ventricle contracts after filling with blood from the left atrium, the walls of the ventricle move inward and release some of the tension from the papillary muscle and chords. The blood pushed up against the under-surface of the mitral leaflets causes them to rise toward the annulus plane of the mitral valve. As they progress toward the annulus, the leading edges of the anterior and posterior leaflet come together forming a seal and closing the valve. In the healthy heart, leaflet coaptation occurs near the plane of the mitral annulus. The blood continues to be pressurized in the left ventricle until it is ejected into the aorta. Contraction of the papillary muscles is simultaneous with the contraction of the ventricle and serves to keep healthy valve leaflets tightly shut at peak contraction pressures exerted by the ventricle.
The native heart valves (such as the aortic, pulmonary, tricuspid, and mitral valves) serve critical functions in assuring the forward flow of an adequate supply of blood through the cardiovascular system. These heart valves can be rendered less effective by congenital, inflammatory, infectious conditions, or other disease. Such damage to the valves can result in serious cardiovascular compromise. Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood or regurgitation through the valve when the leaflets are supposed to coapt together to prevent regurgitation. Valve disease can be severely debilitating and even fatal if left untreated. For many years the definitive treatment for such disorders was the surgical repair or replacement of the valve during, for example, open heart surgery.
Various surgical techniques may be used to repair a diseased or damaged valve, which is typically used on minimally calcified valves. Surgical repair of the native valve is commonly conducted using so-called annuloplasty rings. Examples of annuloplasty rings, including methods of use for repairing native valves, are disclosed in U.S. Pat. No. 4,055,861, filed Apr. 9, 1976 and entitled “Support for a Natural Heart Valve”; U.S. Pat. No. 5,041,130, filed Nov. 30, 1989 and entitled “Flexible Annuloplasty Ring and Holder”; U.S. Pat. No. 6,558,416, filed Mar. 6, 2001 and entitled “Annuloplasty Ring Delivery Method”; and in co-pending U.S. patent application Ser. No. 13/019,506, filed Feb. 2, 2011 and entitled “Devices and Methods for Treating a Heart,” the entire contents of each of which are incorporated herein by reference.
Sometimes actual replacement of the heart valve is the preferred option. Heart valve replacement may be indicated when there is a narrowing of a native heart valve, commonly referred to as stenosis, or when the native valve leaks or regurgitates, such as when the leaflets are calcified. Due to aortic stenosis and other heart valve diseases, thousands of patients undergo surgery each year wherein the defective native heart valve is replaced by a prosthetic valve, either bioprosthetic or mechanical. Prosthetic cardiac valves have been used for many years to treat cardiac valvular disorders.
When the valve is replaced, surgical implantation of the prosthetic valve typically requires an open-chest surgery during which the heart is stopped and patient placed on cardiopulmonary bypass (a so-called “heart-lung machine”). In one common surgical procedure, the diseased native valve leaflets are excised and a prosthetic valve is sutured to the surrounding tissue at the valve annulus. Because of the trauma associated with the procedure and the attendant duration of extracorporeal blood circulation, some patients do not survive the surgical procedure or die shortly thereafter. It is well known that the risk to the patient increases with the amount of time required on extracorporeal circulation. Due to these risks, a substantial number of patients with defective valves are deemed inoperable because their condition is too frail to withstand the procedure. By some estimates, about 30 to 50% of the subjects suffering from aortic stenosis who are older than 80 years cannot be operated on for aortic valve replacement.
Because of the drawbacks associated with conventional open-heart surgery, percutaneous and minimally-invasive surgical approaches are garnering intense attention. In one technique, a prosthetic valve is configured to be implanted in a much less invasive procedure by way of catheterization. For instance, U.S. Pat. No. 5,411,552 to Andersen et al. describes a collapsible valve percutaneously introduced in a compressed state through a catheter and expanded in the desired position by balloon inflation. Although these remote implantation techniques have shown great promise for treating certain patients, replacing a valve via surgical intervention is still the preferred treatment procedure. One hurdle to the acceptance of remote implantation is resistance from doctors who are understandably anxious about converting from an effective, if imperfect, regimen to a novel approach that promises great outcomes but is relatively foreign. In conjunction with the understandable caution exercised by surgeons in switching to new techniques of heart valve replacement, regulatory bodies around the world are moving slowly as well. Numerous successful clinical trials and follow-up studies are in process, but much more experience with these new technologies will be required before they are completely accepted.
In some situations, replacement of the native heart valve with a prosthetic heart valve may be the desired treatment. There are approximately 60,000 mitral valve replacements (MVR) each year and it is estimated that another 60,000 patients should receive a MVR due to increased risk of operation and age. The large majority of these replacements are accomplished through open-heart surgery, where a prosthetic heart valve is surgically implanted with the patient on pulmonary bypass. Such surgically implanted prosthetic valves have a long and proven record, with high success rates and clinical improvements noted after such valve replacement. However, it can be desirable to keep the time that the patient spends on pulmonary bypass to a minimum.
Surgeons relate that one of the most difficult tasks when attempting valve repair or replacement, either in open heart surgeries or minimally invasive heart valve implantations (e.g., through small incisions) is tying the suture knots that hold the valve or repair ring in position. A typical prosthetic mitral valve implant utilizes 12-24 sutures (commonly about 15) distributed evenly around and manually tied on one side of the sewing ring. The implantation process can be very time consuming and difficult to perform, particularly through minimal size incisions due to the numerous pairs of sutures that need to be precisely placed in the annulus and the knots that are typically used to secure the sutures when the valve is parachuted into place. Similarly, in a valve repair procedure numerous pairs of sutures must be precisely placed around the native annulus to attach the repair device. Minimizing or even eliminating the need to use suture (and/or to tie suture knots) for attachment of prosthetic valves or repair devices would greatly decrease the time of the procedure and/or facilitate the use of smaller incisions, thus reducing infection risk, reducing the need for blood transfusions, reducing the time spent on bypass, and allowing more rapid recovery.
Accordingly, there is a need for an improved device and associated method of use wherein a prosthetic valve or valve repair device can be implanted in a more efficient procedure that reduces the time required on extracorporeal circulation and/or catheterization. It is desirable that such a device and method be capable of helping patients with defective valves that are deemed inoperable because their condition is too frail to withstand a lengthy conventional surgical procedure. The present invention addresses these needs and others.